This application claims the priority of 197 08 892.9 filed Mar. 5, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an internal combustion engine with at least one cylinder whose cylinder axis extends at least approximately horizontally in the installed position.
An internal combustion engine of this type is known from German patent document DE 25 42 803 C2. In order to avoid the development of a large quantity of smoke when starting the engine, which depends on certain conditions (piston position, alignment of the engine and/or the vehicle at rest, temperature of the engine when shut off), it is known from DE 25 42 803 to provide recesses on the piston ring grooves that extend to the bottom of the groove and form a labyrinthine passage connected with the interior of the piston by a bore in the groove facing away from the combustion chamber. These recesses allow equalization of the pressure in the combustion chamber, which is a function of the piston position, and the ambient pressure in the crankcase. This passage prevents a pressure that prevails in the combustion chamber of the shutoff engine, said pressure being lower than the ambient pressure, being maintained for a long time after the engine is shut off, and resulting in lubricant being drawn into the combustion chamber. This lubricant that enters the combustion chamber is burned when the engine is restarted and produces an increased amount of smoke. Providing recesses in all the piston ring grooves, however, entails considerable expense. Very precise machining with low tolerances is required, particularly in the area of the first piston ring groove facing the combustion chamber, because of the high loads involved. If such a recess is formed in the first piston ring groove after the surface of the ring has been finished, there is an increased danger of formation of burrs at the transition from the recess to the edge of the ring groove. If on the other hand the ring groove is finished after the recess has been formed, the familiar machining problems caused by the open machining surface at the edge of the recess will result. In addition, such a recess in the vicinity of the first piston ring facing the combustion chamber leads to an undesired increase in blow-by gas flow. In addition, the part of the recess of the first piston ring groove that faces the combustion chamber during operation of the internal combustion engine has a tendency to become clogged by combustion residues. The desired reduction of the amount of oil drawn into the combustion chamber is therefore impeded after the engine has been operating for a while, while at the same time a significant increase in blow-by gas flow persists as a result of the recess on the first piston ring that faces away from the combustion chamber.
Hence there is a need for improvements in an engine having at least one cylinder aligned horizontally in the installation position of the engine such that reduction of blue smoke on starting is achieved at limited machining expense, while at the same time a blow-by gas flow is maintained that is as low as possible.
This and other needs have been met according to the present invention by providing an internal combustion engine, comprising: at least one cylinder having a cylinder axis extending at least approximately horizontally in the installed position, a piston defining at least three annular grooves along an outer circumference and defining an interior chamber; a piston ring disposed in each of the annular grooves, respectively, each piston ring having an at least approximately rectangular cross section, annular chambers being defined between the piston and the cylinder between adjacent ones of the piston rings, recesses being defined in the piston adjacent at least two of the annular grooves, each said recess extending between a bottom of the respective annular groove and the outer circumference of the piston and communicating with one of said annular chambers, at least one bore defined in the piston between the bottom of the annular groove located remote from a combustion chamber and the interior chamber of the piston, the annular groove closest to the combustion chamber being free of recesses, an axial play between the annular groove closest to the combustion chamber and the piston ring disposed therein being at least 50 .mu.m.
This and other needs have also been met according to the present invention by providing a piston for a horizontal cylinder of an internal combustion engine, said piston comprising: a piston bottom to be faced to a combustion chamber of the engine; a piston body integral with said piston bottom and extending in an axial direction from said piston bottom, an interior of said piston body and said piston bottom defining an interior chamber; at least three annular grooves being defined in said piston body extending circumferentially around the piston, a first of said annular grooves located nearest said piston bottom having a constant cross-section in said axial direction throughout, said first annular groove being dimensioned to receive a piston ring with an axial play between the piston ring and the first annular groove of at least 50 .mu.m, a second and a third of said annular grooves located further from said piston bottom having a cross-section which varies in said axial direction at recesses extending from an outer circumference of said piston to a bottom of said annular grooves, at least one bore defined in the piston communicating the annular groove located furthest from the piston bottom with the interior chamber.
By designing the first piston ring groove (closest to the combustion chamber) without a recess, the seal between the combustion chamber relative to the prior art is improved so that the blow-by gas flow is significantly reduced. At the same time, the tuned geometry of the piston ring and the axial play, which is relatively large by comparison to conventional piston ring geometries, permit pressure equalization between the combustion chamber and the annular chamber between the first and second piston rings. The second and third piston ring grooves can then be provided with recesses without a significant increase in blow-by gas flow, forming a labyrinthine passage connected by bores between the bottom of one of the annular grooves facing away from the combustion chamber and the interior of the piston. With this design of the piston rings and piston ring grooves, the machining cost for the piston is significantly reduced. In particular, the first piston ring groove that is subjected to very high stress can be machined completely without costly edge machining processes being required.
If recesses are formed in a piston ring groove on both sides of the piston ring, these recesses can advantageously be located opposite one another, simplifying machining because both recesses can be produced by a common drilling and/or grinding process for example.
Possible penetration of lubricant into the combustion chamber is prevented especially effectively when the second piston ring from the combustion chamber is prevented from twisting. This ensures that the face of the piston ring is always uppermost. The lower area over which the piston travels is therefore reliably sealed off so that penetration of lubricant along the lower wall is effectively prevented when the cylinder is inclined.
Such protection against twisting can be achieved in an especially advantageous manner by initially bending portions of one of the two ring faces in the axial or radial direction, with the bent section then cooperating with a recess in the annular groove that receives the piston ring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.